Some heat exchangers operate by transmitting fluid through a conduit and passing cool air over that conduit. For example, a heat exchanger may include a pipe that enters into a flow path, and then forms a coil before exiting out of the flow path. The heat exchanger may also be a plate type or any other type of indirect heat exchanger. Air, typically cool air relative to the indirect heat exchanger, passes over the coil, which uses convection principals to facilitate the indirect exchange of heat between the fluid and the air.
To increase the efficiency of this process, some heat exchangers use a “wet” process that dispense evaporative liquid, such as water, over the coils. This invokes the principals of evaporation to further increase the rate of heat transfer from the fluid. For instance, an evaporative indirect heat exchange process can operate about five times more efficiently than a dry heat exchange process. However, in some situations it may be desirable to conserve use of evaporative liquid, and thus restrict, limit, or control use of a heat exchanger in wet process. In such situations, it may make sense to operate the heat exchanger intermittently in wet and dry modes.